The objective of this proposal is to define signal transduction pathways that control neuronal differentiation. Our studies with cultured PC12 pheochromocytoma cells, an established model for analysis of nerve growth factor (NGF)- dependent signaling pathways that control neural differentiation, indicate the integration of the extracellular signal-regulated kinase (ERK) and cJun N- terminal kinase (JNK) families of mitogens-activated protein (MAP) MAP kinases and specific CREB and Jun family members in neuron-specific gene induction. We have recently established the conditions for in vitro neuronal differentiation of multipotent murine embryonic development and the resulting neurons are highly representative of their in vivo-generated counterparts. The ability to generate neurons for ES cells derived from mice in which genes encoding MAP kinase components and transcription factor targets are homozygously deleted provides a powerful genetic approach to signal transduction of neuronal differentiation. We hypothesize that integration of distinct MAP kinase signaling pathways and their specific transcription factor targets serve as a molecular switch to induce multiple genes required for acquisition of the neural phenotype. To test this hypothesis, we will complete these specific aims: Aim 1. Identify the signaling pathways that induce the NFLC gene during neuronal differentiation of PC12 cells and ES cells. Aim 2. Define the regulatory elements within the neuronal differentiation. Aim 3. Define the role of the signal pathways and transcription factors that regulate the NFLC promoter as a molecular switch involved in the induction of multiple neural-specific genes in PC12 and ES cells. MAP kinases have been extensively analyzed in the context of mitogenesis, but not differentiation. Completion of these aims will elucidate the mechanism by which these signal pathways can regulate the transcription of genes required for cell differentiation, a comparatively understudied research area.